Note for Green Technology - GT By Ruparani Mahapatra
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Module 1(Part1) GLOBAL WARMING AND ITS EFFECT Introduction. Climate change is threatening plants, animals and their habitats. Research reveals that temperature changes and other shifts in climate are impacting plant growth stages, affecting migration patterns, threatening species survival and affecting water quality, among other factors. Temperatures are rising, snow and rainfall patterns are shifting, and more extreme climate events – like heavy rainstorms and record high temperatures are happening. Many of these observed changes are linked to the rising levels of carbon dioxide and other greenhouse gases in our atmosphere, caused by human activities. Physical definition of global warming Earth receives energy that travels from the sun in a variety of wavelengths, some of which we see as sunlight and others that are invisible to the naked eye, such as shorter- wavelength ultraviolet radiation and longer-wavelength infrared radiation.As this energy passes through Earth’s atmosphere, some is reflected back into space by clouds and small particles such as sulphates; some is reflected by Earth’s surface; and some is absorbed into the atmosphere by substances such as soot, stratospheric ozone, and water vapour. The remaining solar energy is absorbed by the Earth itself, warming the planet’s surface. Certain gases, such as CO2, CH4 and water vapour, work like a blanket to retain much of that heat.. The gases do this by absorbing the heat and radiating it back to Earth’s surface. These gases are nicknamed “greenhouse gases” because of their heat-trapping effect. Global warming is defined as an increase in the average temperature earth due to green house effect caused by greenhouse gases like CO2, CH4 water vapour.
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The present warming is generally attributed to increase in the greenhouse effect, brought about by inc reased levels of greenhouse gases, largely due to the effectsof human industry and agriculture. The new Carbon Problems Dry air on the earth consists of nitrogen (78%), oxygen (21%),argon (0.9%), carbon dioxide(0.03%) and other gases to a smaller extent. The relative proportion of each constituent varies in air from one region to another region depending on the activity predominates in that place. The major gases emitted from human and animal activities are carbon dioxide,(77%), nitrous oxide/(14%)methane(8%), hydro fluorocarbons(HFCs),per fluorocarbons(PPCS) and sulphur hexafluoride(SF6). Out of which the first three gases are responsible for global warming and rest three are causing ozone layer depletion. Water vapour also contributes to increase in atmospheric temperature. CO2 is an important heat-trapping (greenhouse) gas, which is released through human activities such as deforestation and burning fossil fuels, as well as natural processes such as respiration and volcanic eruptions. The major sources of green house gases are • • • • • Natural sources: Animal and plant respiration, anaerobic decomposition of organic matter fermentation from animal bleaching. Industrial chemicals and solvent manufacturing process. Power generation and power use by using fossil fuels Transport: Traffic by road, rail, air, sea and air by using fossil fuels like oil, petrol etc. Agricultural activities release carbon dioxide, methane etc. UN framework convention on climate change (UNFCCC) was started in March 1994 whose signatories are required to prepare an inventory of green house gases and their removal by sinks in accordance with specified methodologies On the global basis the percentages of emission from different major sources are as follows source Percentage(%) Electricity anf heating 24.8 Deforestation and other land use 20.6 Transportation 14.5 Industry 12.8 Aagriculture 13.5 Other fuel burning 9.0 Fugitive emission 3.4 Waste 1.6 The list helps to bring out clearly that deforestation release more carbon dioxide than the transport sector or the industrial sector Accumulation CO2 remains in the atmosphere longer than the other major heat-trapping gases emitted as a result of human activities. It takes about a decade for methane (CH4) emissions to leave the atmosphere (it converts into CO2) and about a century for nitrous oxide (N2O). After a pulse of CO2 is emitted into the atmosphere, 40% will remain in the atmosphere for 100 years and 20% will reside for 1000 years, while the final 10% will take 10,000 years to turn over. Net accumulation of green house carbons (GHCs) can be expressed in terms of CO2 equivalent contained in the atmosphere. It is given by ∑sources of CO2- ∑sinks of CO2= net accumulation
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It does not matter where the source is located or where the sink is located. Both are part of the overall atmosphere around the earth and the earth is revolving. As the half life of CO2 is long, it takes a long time dying out. The developed countries have occupied 70% of the carbon space though their population is only 20%. Long Half- life The gases like CO2, CH4, N2O, H2O, CFCs, HFCs etc collectively called green house gases released by different activities were accumulating in the atmosphere and leading to a slow change in the climate which is a very important phenomenon affecting our lives.CO2 contributed more than any driver in climate change between 1975 to 2011.As per the Intergovernmental Panel on Climate Change (IPCC) the positive radiative forcing” (RF) value of CO2 is the highest among all GHGs. Other gases have more potent heat-trapping ability molecule per molecule” (RF) than CO2 (e.g. methane), but are simply far less abundant in the atmosphere. The CO2 has a half life of about 120-150 years. That means the carbon dioxide released about 120 years ago is still there in the atmosphere. The accumulation will increase at a faster rate with increase in population and industrialisation. In 2005 the CO2 concentation in the atmosphere was estimated to be 385ppm and it is increasing at a rate of 2 to 3 ppm per year. Heating Potential Global warming potential (GWP) is a measure of how much heat a greenhouse gas traps in the atmosphere up to a specific time horizon, relative to carbon dioxide. It compares the amount of heat trapped by a certain mass of the gas to the amount of heat trapped by a similar mass of carbon dioxide and is expressed as CO2 equivalent (CO2s GWP is standardized to 1). A GWP is calculated over a specific time horizon, commonly 20, 100, or 500 years, the time horizon can greatly affect the numerical values obtained for CO2 equivalents. In the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, methane has a lifetime of 12.4 years and with climatecarbon feedbacks a global warming potential of 86 over 20 years and 34 over 100 years in response to emissions. For a change in time horizon from 20 to 100 years, the GWP for methane therefore decreases by a factor of approximately 2.5. The GWP depends on the following factors: • the absorption of infrared radiation by a given species • the spectral location of its absorbing wavelengths • the atmospheric lifetime of the species Thus, a high GWP correlates with a large infrared absorption and a long atmospheric lifetime. The dependence of GWP on the wavelength of absorption is more complicated. Even if a gas absorbs radiation efficiently at a certain wavelength, this may not affect its GWP much if the atmosphere already absorbs most radiation at that wavelength. Calculating the global warming potential Radiative forcing provides a simplified means of comparing the various factors that are believed to influence the climate system to one another; global warming potentials (GWPs) are one type of simplified index based upon radiative properties that can be used to estimate the potential future impacts of emissions of different gases upon the climate system in a relative sense. The GWP is defined as the ratio of the time-integrated radiative forcing from the instantaneous release of 1 kg of a trace substance relative to that of 1 kg of a reference gas. The radiative forcing capacity (RF) is the amount of energy per unit area, per unit time, absorbed by the greenhouse gas that would otherwise be lost to space. It can be expressed by the formula: RF= ∑Absi.Fi (pathlength.density) i = an interval of 10 inverse centimetres. ,Absi = integrated infrared absorbance of the sample in that interval,
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Fi = RF for that interval (IPCC) provides the generally accepted values for GWP, which changed slightly between 1996 and 2001. Carbon Emission Factors Evaluation of carbon emissions is essential to studying carbon related issues. Emission factors assume a linear relation between the intensity of the activity and the emission resulting from this activity: Emission pollutant = Activity * Emission Factor pollutant Intensities are also used in projecting possible future scenarios such as those used in the IPCC assessments, along with projected future changes in population, economic activity and energy technologies. The interrelations of these variables are treated under the so-called Kaya identity. The level of uncertainty of the resulting estimates depends significantly on the source category and the pollutant. Some examples: • (CO2) emissions from the combustion of fuel can be estimated with a high degree of certainty regardless of how the fuel is used as these emissions depend almost exclusively on the carbon content of the fuel, which is generally known with a high degree of precision. • Sulphur dioxide (SO2), since sulphur contents of fuels are also generally well known. • Levels of other air pollutants and non-CO2 greenhouse gas emissions from combustion depend on the precise technology applied when fuel is combusted. These emissions are basically caused by either incomplete combustion of a small fraction of the fuel (carbon monoxide, methane, nonmethane volatile organic compounds) or by complicated chemical and physical processes during the combustion and in the smoke stack or tailpipe. Examples of these are particulates, NOx, a mixture of nitric oxide, NO, and nitrogen dioxide, NO2). • Nitrous oxide (N2O) emissions from agricultural soils are highly uncertain because they depend very much on both the exact conditions of the soil, the application of fertilizers and meteorological conditions. The factors are given in ranges because the actual emissions depend on the chemical composition of the substance and the efficiency with which it is burnt and the efficiency of ignition device.. Carbon absorption in nature Climate change has been linked to the accumulation of excess carbon dioxide in the atmosphere.In an efficient ecosystem the carbon production is balanced by carbon absorption in nature so that the recycling can go on. Several ways are there in which carbon released to the atmosphere is absorbed back in nature making a cyclic turnover from time to time are called as the sink. These are trees, grass, forest, soil, peat, permafrost, ocean waters, carbonate deposits in deep oceans and natural sequestration process. Photosynthesis is a process that converts light energy into the organic molecules of biomass which is composed of mainly carbohydrates symbolized as CH2O. In this process the oxygen produced is about 1.6 times of the weight of the algae produced by photosynthesis. About 14% of oxygen produced through photosynthesis is consumed back in respiration and rest helps all living things to survive. Carbon sequestration, the long-term storage of carbon in plants, soils, geologic formations, and the ocean. It occurs both naturally and as a result
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